The invention is based on an electromagnetically actuatable injection valve as defined hereinafter. U.S. Pat. No. 4,934,605 has already disclosed an electromagnetically actuatable injection valve that has a valve needle which upon excitation of a magnet coil is pulled against a core by an armature joined to the needle, causing the valve needle, with a sealing seat formed on it, to lift away from a conical valve seat face embodied on a nozzle body. The valve needle has a terminal cone adjoining a cylindrical segment in the flow direction, and this cone in turn changes into an again-cylindrical terminal protrusion. The sealing seat is embodied as a rounded area at the transition between the cylinder segment and the terminal cone. The contour of the rounded area traces an external jacket face of an imaginary torus, with a longitudinal valve needle axis as its center point.
Metering the fuel is done in injection ports, which are disposed in a perforated plate that covers a downstream terminal opening of the nozzle body.
The narrow annular gap between the valve needle and the valve seat face that is exposed upon opening of the injection valve leads to high flow velocities of the fuel. The flow losses that occur in the annular gap because of the viscosity of the fuel depend linearly on the flow velocity, so that a high flow velocity in the annular gap leads to a high pressure loss in the fuel flow.
Because of the geometry of the valve needle, the pulse flow vector of the fuel flow is oriented strongly in the direction of the injection ports over the entire path between the annular gap and the injection ports, resulting in anisotropic distribution of the fuel quantity injected through the various injection ports.
Tests of the injection valve with substitute fluids for commercially available fuel have been carried out in order to record characteristic curves and to test the operating performance. If accurate statements on the injection valve are to be made from these model tests, the hydraulic similarity must remain assured despite the different parameters of the substance, such as the viscosity of the substitute fluid. The orientation of the pulse flow vector of the fuel flow in the direction of the injection ports over the path between the annular gap in the injection ports makes it more difficult to maintain the hydraulic similarity when substitute fluids are used.